Optoelectronic devices in which a resonance between optical fields and tunneling electrons is used to modulate the flow of said electrons

ABSTRACT

An apparatus for high speed gating of electric current based on the resonant interaction of tunneling electrons with optical fields is disclosed. The present invention biases an electron-emitting tip with a DC voltage source and focuses an output from a laser on the electron-emitting tip to stimulate electron emission from the tip. The electron emission creates an electrical signal that is coupled to circuitry for further processing. In accordance with the present invention, various methods of coupling the electrical signal from the electron-emitting tip are disclosed, as are various methods of reducing the magnitude of the laser output needed to stimulate electron emission, and methods of enhancing the static current density.

RELATED APPLICATION

This application claims priority from provisional application Serial No.60/072,389, filed Jan. 9, 1998.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates generally to optoelectronics and, moreparticularly, to an optoelectronic device based on electric currentgating due to resonant interaction of tunneling electrons with opticalfields.

(b) Description of Related Art

Optically-gated electrical switches, such as Auston switches, arecommonly used in the generation of high frequency terahertz (THz)signals. Optically-gated switches typically include an optical pulsegenerator (e.g., a laser) and a photoconductor switch mounted on aminiature antenna. When the optical pulse generator is active, it emitsan optical field that is focused on the photoconductor switch. Thephotoconductor switch conducts current in response to the optical field.Rapid switching of the optical pulse generator and the associatedswitching of the current through the photoconductor switch cause theantenna to emit high frequency signals. The miniature antenna couplesthe high frequency signal from the photoconductor switch to othercircuitry that utilizes or processes the high frequency signal.

The switching speed of an optically-gated electrical switch is limitedby the photoconductor switch and not by the optical pulse generator.Optical pulses having 50 femptosecond (fs) pulse widths may be producedby commercially available TI:Al₂ O₃ lasers from various manufacturers(e.g., Coherent Laser Group and Spectra Physics). Optical pulses asshort as 6 fs have been experimentally produced using cubic phasecompensation. Pulses of this duration correspond to electrical signalshaving a frequency of approximately 100 THz. However, these switchingspeeds are not realizable due to the relatively slow response of thephotoconductor switches.

Another application of optoelectronic devices is photomixing.Photomixing uses two lasers and a material having non-linear opticalproperties to generate a signal at the difference frequency. Forexample, two Ti:Al₂ O₃ lasers may be focused on an epitaxial layer ofgallium arsenide (GaAs). The interaction of the two lasers and the GaAssubstrate creates a difference frequency signal based on the differencebetween the laser frequencies. The epitaxial GaAs substrate may belocated at the driving point of a miniature antenna that couples thedifference frequency signal to other circuitry for processing.Typically, these devices have an output power less than 1 microwatt at 1THz, and a roll off rate of 12 dB per octave.

A major effort is being made at several laboratories to developmicrowave amplifiers based on field emitter arrays (FEA). These devicesoperate as triodes, in which a gate electrode controls the current.These devices have a unity gain bandwidth of less than 2 GHz because theinput is shunted by the gate capacitance. The use of lasers to gateelectron emission from a field emitter array (FEA) is also a topic ofcurrent research. Current experiments have used a Nd:YAG pulsed laseroperating at a wavelength of 1 micrometer(μm) to stimulate electronemission from an array of emitting tips. The emitting tips were madefrom silicon tantalum disilicide and were coated with gold. The laserbeam was focused to a diameter of 3 mm or 4 mm on the emitting tips,with the optical propagation vector in the plane of the tips. Thelaser's pulse width was 5 nanoseconds (ns). When the power flux densityof the laser was 2.7×10¹¹ W/m², a pulsed current was emitted from thetips. There was no pulse of current when a lower power flux density wasused, and when the power flux density was increased to 4.2×10¹² W/m² thetips fused due to the intense heat from the process. However, thecurrent pulse was only present when a gold tip coating was used, whichsuggests that the current pulse may be due to ions caused byfield-induced evaporation. The minimum duration for a current pulseobtained in this manner is 2 nanoseconds (ns). This design requires thelaser to supply a pulsed power of at least 2 megawatts (MW) to produce adetectable current pulse. This laser power level is not practical formost optical switching and mixing applications.

Accordingly, there is a need for new devices having bandwidths muchgreater than 1 THz, but this has not been possible with priorconfigurations. The performance of prior configurations is limited bythe magnitude and frequency dependence of the nonlinear response ofavailable materials. The performance of prior configurations based onfield emission has also been limited by the use of a triodeconfiguration. Additionally, prior configurations require extremely highoptical power to produce detectable current emission.

SUMMARY OF THE INVENTION

The present invention may be embodied in an optoelectronic deviceincluding an evacuated chamber containing a negatively-biased sourceelectrode having a pointed tip for emitting electrons and a coating forenhancing the effect of an optical field impinging on the sourceelectrode, a laser generator for emitting an optical field that isfocused on the pointed tip of the source electrode for stimulatingemission of rapidly varying electrical current from the pointed tip ofthe source electrode, and means responsive to the rapidly-varyingelectrical current for coupling the signal produced by said currentoutside of said evacuated chamber.

In accordance with the present invention the optical field from thelaser generator has a resonant interaction with the pointed tip.Additionally, the source electrode may be fabricated from variousmaterials such as tungsten, molybdenum, iridium, titanium, zirconium,hafnium, aluminum nitride, gallium nitride, diamond-like carbon,molybdenum silicide, and refractory metal carbides such as zirconiumcarbide or hafnium carbide. These materials may be used either singly orcombined as in coatings. The pointed tip may also includemicro-protrusions, macro-outgrowths, supertips, and ultrasharp fibrilsto increase the local curvature of the surface.

To enhance the effect of the optical field, a coating may be depositedon the pointed tip. This coating may include silver, aluminum orgallium.

In accordance with the present invention, the coupling means may includea Goubau line, a traveling wave log-periodic antenna or a dielectricwaveguide. The dielectric waveguide may be fabricated from quartz,aluminum nitride, silicon, germanium or diamond-like carbon.

The invention itself, together with further objects and attendantadvantages, will best be understood by reference to the followingdetailed description, taken in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of an optical mixer including a Goubau line of thepresent invention;

FIG. 2 is a diagram of an alternate embodiment of an optical mixerincluding a traveling wave log-periodic antenna in accordance with thepresent invention;

FIG. 3 is a diagram of an alternate embodiment of an optical mixerincluding a dielectric waveguide in accordance with the presentinvention; and

FIG. 4 is a diagram of a high speed switch in accordance with thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is based on laser-assisted field emission ratherthan the nonlinear response of materials. The increased switching speedof the present invention is possible in part because of the extremelyhigh values of the current density (˜10⁹ A/m²) and extraction field(˜10V/nm), and the extremely short length of the interaction (˜1 nm).These parameters far exceed the parameters that may be achieved usingsemiconductor technology.

Experimentation and simulations have revealed a quantum resonance in theinteraction of optical fields with tunneling electrons. This resonantinteraction causes an increase in the signal current by approximately 30dB. The mechanism for this resonance is reinforcement of the wavefunction by reflections at the classical turning points for electrons inthe potential barrier. Thus, for the case of a square potential barrier,the resonance occurs when an electron is promoted above the potentialbarrier by absorbing one quantum from the optical field and when thelength of the barrier is an integral multiple of one-half of theDeBroglie wavelength. In laser-assisted field emission the opticalwavelength for resonance depends on the applied static field, thematerial used for the emitting tip, and the temperature. For example,with tungsten at room temperature, the resonance is at 500 nm with 6V/nm and 400 nm with 5 V/nm.

By way of example, the optoelectric devices of the present inventionwill be described as a source electrode having a pointedelectron-emitting tip and a collector, sealed within an evacuatedchamber. A DC voltage source is connected between the pointedelectron-emitting tip and the collector to create a static electricfield. In accordance with the present invention, the emitting tip isirradiated with an optical field from a laser generator source. Theoptical field causes the electric vector of the radiation field to besuperimposed on the applied static field, thereby changing the height ofthe potential barrier at the surface of the tip. Thus, the probabilityof electron emission by quantum tunneling is increased. The interactionbetween the optical energy and the electrons emitted by the pointedelectron-emitting tip may be referred to as a resonant interaction. Theoptical fields cause a rapid variation in the current or signal emittedat the surface of the source electrode. The power of the current orsignal emitted at the surface of the source electrode is proportional tothe square of the static current and the square of the power fluxdensity of the optical field. To effectively utilize this resonanteffect, efficient means are required to 1) increase the density of thestatic current, 2) increase the effect of the laser on the emittedcurrent, and 3) couple the high frequency energy to the load from thetip surface where the signal is generated. In accordance with thepresent invention, a number of different configurations are proposedthat meet these requirements. The optoelectric devices of the presentinvention may be embodied in optical mixers or high speed switches thatare gated by optical pulses.

FIGS. 1-3 illustrate three embodiments that use the present inventionfor photomixing. Photomixing is a process that is used to generate highquality signals that are tunable over an extremely large bandwidthwithout the use of high-speed electrical drivers. In accordance with thepresent invention, the mixing signal may be modulated by superimposingan information-carrying signal on the DC bias of the tip. Additionally,modulation may be accomplished through modulation of one or more of theoptical sources. Each of the embodiments shown in FIGS. 1-3 may also beused to mix a single optical source with an external optical source toaccomplish homodyne and heterodyne detection in coherent optical fiberand optical beam communications at extremely high data rates. Moreover,the present invention may be used in applications with a single opticalsource that is mode-locked or Q-switched to produce short optical pulsesat a highly stable repetition rate. Such a device would respond to therepeated short optical pulses by generating a frequency comb atharmonics of the repetition frequency.

Referring now to FIG. 1, a photomixer using a Goubau line to couple theemitted signal from the evacuated chamber is shown. The photomixer shownin FIG. 1 includes an evacuated chamber 50, which contains a sourceelectrode 55 and a collector 60. To increase the static current density,the source electrode 55 may be fabricated from various materials such astungsten, molybdenum, iridium, titanium, zirconium, hafnium, aluminumnitride, gallium nitride, diamond-like carbon, molybdenum silicide, andrefractory metal carbides such as zirconium carbide or hafnium carbide.These materials may be used either singly or combined as in coatings.The source electrode 55 includes a pointed electron-emitting tip 65,which may include features such as micro-protrusions, macro-outgrowthsor super tips. These features may be created using well known heatingtechniques, electron deposition or other techniques known to thoseskilled in the art. The purpose of these features is to increase thelocal curvature by roughening the tip 65. These features increase thestatic current density by as much as 20 dB.

The pointed electron-emitting tip 65 is coupled to a Goubau line 70,which in turn is connected to a horn transition 75. External circuitry80 is used to appropriately bias the emitter and the collector. Theexternal circuitry includes a DC voltage source 85, a current limitingresistor 90, an RF choke 95, a coupling capacitor 100, and a load 105.Additionally, the photomixer includes optical components 110, which areused to irradiate the pointed electron-emitting tip 65 with an opticalfield. The optical components 110 include two laser diodes 115, 120 eachmounted on piezoelectric transducer positioners 125, 130, a beamsplitter 135, a lens system 140, and a spherical mirror 145 mounted on apiezoelectric transducer 150.

During mixer operation, the DC voltage source 85 negatively biases thesource electrode 55 and positively biases the collector 60. The currentlimiting resistor 90 is provided to limit the amount of current that issourced by the DC voltage source 85. When the source electrode 55 isproperly biased, an optical field emitted by the laser diodes 115, 120is combined using the beam splitter 135 and focused on the pointedelectron-emitting tip 65 using the lens system 140.

External cavity lasers could be used to obtain a stable single-lineoptical field for photomixing in a compact device. An external cavitylaser is a laser diode in which a reflecting surface of the internalcavity is replaced by an external mirror or grating to obtain a greatercavity length. The external cavity configuration makes it possible toseparate various lines of radiation from the laser. The disadvantage toexternal cavity lasers is the fact that the output of the externalcavity is typically less than 10% of the output from the laser itself.This derating is due to the fact that the external cavity must have ahigh quality factor, so the power removed from it must be a smallfraction of the output from the laser. In accordance with the presentinvention, the external laser cavity is preferably integrated with theevacuated chamber 50. This configuration increases the coupling of theoptical fields to the electron-emitting tip 65 by approximately 20 dB.Additionally, in a preferred embodiment, the angle between thepropagation vector of the optical field and the axis of the pointedelectron-emitting tip 65 is approximately 15°. This configurationenhances the effect that the optical field has on the emission from thepointed electron-emitting tip 65 by as much as 30 dB.

The spherical mirror 145 re-focuses and reflects the optical field fromthe lasers 115, 120 back to the lens system 140, thereby irradiating theelectron-emitting tip 65 on the return path. The lasers 115, 120 and thespherical mirror 145 are mounted on piezoelectric transducer positioners(PZTs) 125, 130, 150. The PZTs 125, 130, 150 are used to adjust thepositions and of the laser diodes 115, 120 and the spherical mirror 145in response to applied voltages. The PZTs 125, 130, 150 are used toadjust the size of the external cavities and thereby shifting thefrequency of the mixing signal in response to the voltage applied to thePZTs 125, 130, 150. Voltages applied to the lasers 115, 120 may also beused to modulate the lasers, thereby modulating the mixing product.

The optical fields cause a rapid variation in the emitted current at thesurface of the source electrode, thereby creating a signal. However, theextremely high frequency components of the signal decay rapidly as thesignal propagates along the pointed tip 65 due to attenuation anddispersion. Also, the spread of velocities in the emitted electronscauses bunching of the emitted signal to be dispersed as the electronsmove a short distance from the pointed tip 65 toward the collector 60.Thus, it is necessary to use an efficient means to couple the highfrequency energy from the pointed tip 65 to the load 105.

In accordance with the present invention, the optical field iscontrolled to operate in resonance with the pointed electron-emittingtip 65, which is coated with materials such as silver, aluminum, andgallium to create surface plasmons. Surface plasmons increase the localintensity of the optical field by as much as 60 dB, thereby enhancingthe effect of the optical field and reducing the output powerrequirements on the laser diodes 115, 120. The combination of the DCbias and the resonant optical field causes electron emission from thepointed electron-emitting tip 65. The electrons are emitted toward thepositively-biased collector 60. The emission of the electrons generatesa signal at the surface of the pointed electron-emitting tip 65. Thissignal propagates as a Sommerfeld wave, which is a surface wave that isloosely bound to an imperfect conductor. Preferably, during manufacturea thin coating of low-loss dielectric is deposited on the sourceelectrode 55, beginning near the apex of the tip 65 and continuing at anincreasing thickness to provide a transition to the Goubau line 70. AKlopfenstein impedance taper or other related methods may be used totransition from the pointed electron-emitting tip 65 to the Goubau line70. As the Sommerfeld wave reaches the Goubau line 70, it transitionsinto a Goubau wave, which is a surface wave that requires a dielectriclayer for propagation. The Goubau wave is more closely bound to the tipthan the Sommerfeld wave and has considerably less radiation loss.

As the Goubau wave propagates on the Goubau line 70, the DC currentpasses through the conductor under the dielectric of the Goubau line 70.The horn transition 75 is mounted at the end of the Goubau line 70 andis used to make the transition between the high impedance of the Goubauline and the low impedance of a coaxial line, which couples the signalsto the external load 105. The load 105 may be circuitry that furtherprocesses the signal in accordance with a specific application. The RFchoke 95 is used to block the RF signals from the horn transition 75from entering the DC voltage source 85. Similarly, the couplingcapacitor 100 is used to block the DC voltage signal from entering theload 105.

The design of a Goubau line 70 and the horn transition 75 from theGoubau line 70 to the coaxial line are known. Goubau line 70 with a horntransition 75 is useful for frequencies from 10 GHz to 10 THz. The lowerlimit of operation is set by the size of the horn transition 75. Theupper limit of operation is set by excessive ohmic loss caused by thesmall size and high resistance of the metal conductor. At low operatingfrequencies, the horn transition 75 and the Goubau line could beself-supporting or connected to the evacuated chamber 50 usingfilaments. At higher frequencies, however, these structures could besupported using membrane technology or filament technology to limitfield perturbations caused by the supports. For example, a thindielectric membrane of silicon-oxynitride of about 1 μm thick could beused to support the horn transition 75 and the Goubau line 70.

FIG. 2 is a diagram of an alternate embodiment of a photomixer, whichincludes a transmitting traveling wave log-periodic antenna 155 and areceiving log-periodic antenna 160 for coupling signals from theevacuated chamber 50 to the load 105. In the embodiment shown in FIG. 2,the transmitting traveling wave log-periodic antenna operates inbackfire mode. The signals generated at the pointed electron-emittingtip 65 decay rapidly as they propagate. Therefore, the transmittingantenna 155 is located close to the pointed electron-emitting tip 65.The transmitting antenna 155 is designed to have high radiationresistance because the signal current feeding the transmitting antenna155 is very small. The transmitting antenna 155 also has high directivegain. Additionally, the transmitting antenna 155 also has a widebandwidth because of its log-periodic structure.

A log-periodic antenna has three regions of operation: the transmissionregion, the active region, and the unexcited region. The physicallocation of these regions on the antenna is dependent on the frequencyat which the antenna is operated. For example, as the frequency ofoperation is increased, the active region shifts toward the portion ofthe log-periodic antenna having smaller dimensions. In accordance withthe present invention, the high-frequency portion of the antenna ispositioned closest to the pointed electron-emitting tip 65. Thisplacement effectively increases the bandwidth of the system because thehighest frequency signals, which attenuate most rapidly, have theiractive region closest to the pointed electron-emitting tip 65. In apreferred embodiment, metal strip or planar forms of the traveling wavelog-periodic antennas 155, 160 are used to lessen the attenuation. It ispossible to further decrease the ohmic loss by shaping the surface ofthe antenna to add conductive ridges that are oriented to follow thedirection of current flow. In a preferred embodiment, the transmittingand receiving log-periodic antennas are embodied in metal striptriangular-tooth or planar trapezoidal-tooth log-periodic antennas. Foreffective power transfer from the transmitting antenna 155 to thereceiving antenna 160, it is necessary to use small tooth angles toincrease the number of elements in the active region and therebyincrease the radiation resistance of the antennas 155, 160.Alternatively, the log-periodic antenna may be constructed from wire. Ifwire is used, its radius is preferably tapered from 50-100 nm at thehigh frequency portion of the antenna to much larger radius values forregions in the low frequency portion.

Optionally, the present invention may include quasi-optical devices suchas mirrors or lenses may be added to increase the coupling and correctfor changes of the antenna pattern with frequency. For example, anellipsoidal mirror 162 is especially appropriate because radiation fromone focus (the antenna at the emitting tip) is exactly transferred tothe second focus (the antenna at the load) without any distortions oraberrations. That is, the active portion of the transmitting antenna 155is located at one focus of the mirror 162 and the receiving antenna 160is located at the other focus of the mirror 162. The mirror 162increases the coupling of in-phase radiation from the transmittingantenna 155 to the receiving antenna 160, thereby increasing theeffective directivity of the transmitting and receiving antennas.

The embodiment shown in FIG. 2 is suitable for operation at frequenciesbetween approximately 10 GHz and 100 THz. Traveling wave log-periodicantennas such as those described in conjunction with the preferredembodiment may have a directive gain in excess of 10 dB and a radiationresistance of 400Ω or more.

FIG. 3 is a diagram of an alternate embodiment of a photomixer, whichincludes a dielectric waveguide 165 for coupling energy from theevacuated chamber 50 to the load 105. Preferably, the dielectricwaveguide 165 is a dielectric ribbon waveguide having low loss over morethan an octave of frequency operation.

The embodiment shown in FIG. 3 does not use a beam splitter as shown inthe embodiments in FIGS. 1 and 2. Rather, the embodiment in FIG. 3 usestwo lasers 115, 120 and two spherical mirrors 145. This configurationmay be used as an alternative to the beam splitter and single sphericalreflector configuration shown in FIGS. 1 and 2.

The dominant mode for dielectric ribbon waveguide 165 propagation hasthe electric field normal to the broad face of the waveguide. Thedominant mode of propagation in a Goubau line has a radial electricvector. Therefore, the wave on the dielectric waveguide may be launchedfrom the pointed electron-emitting tip 65 using a two stage transition.The first stage consists of a dielectric layer 170 starting near thepointed electron-emitting tip 65 and has an increasing thickness for atransition from the Sommerfeld wave to the Goubau wave. The second stageof the transition consists of a slit in the dielectric along the axis ofthe guide. The slit dielectric is peeled from the metal tip to form aflat dielectric ribbon for a transition from a Goubau wave to adielectric waveguide 165. The metal continues as a DC coupling wire 175.A cylindrical dielectric waveguide may be used in place of thedielectric ribbon, in which case the DC coupling wire 175 is bent sothat it leaves the axis of the guide and is coupled to the DC voltagesource 85.

It is essential to add a choke to prevent the emitted signal fromcoupling to the DC voltage source 85. At low operating frequencies thischoke may be embodied in an inductor or a coil. At high frequencies,however, this choke may be embodied in a sudden change in the impedanceof the DC voltage coupling wire 175. A sudden change in the radius ofthe DC voltage coupling wire 175 is typically a sufficient choke at highfrequencies. In either case, it is preferred to have the choke locatednear the transition between the DC coupling wire 175 and the tip.

At low frequencies the dielectric waveguide 165 and its associatedstructure could be self-supporting. At higher frequencies the dielectricwaveguide 165 and its associated structures may be supported usingmembrane technology or filament technology. The embodiment shown in FIG.3 is useful at operating frequencies between 10 GHz and 100 THz.However, the composition of the dielectric coating must be chosen basedon the frequency of operation. For example, quartz functionssatisfactorily as a dielectric from DC to 4 THz, aluminum nitride isusable from DC to 40 THz. Silicon dielectric is functional from DC to200 THz except for a narrow absorption band near 17 THz. Germanium isuseful from DC to 8 THz and from 15 THz to 150 THz. A diamond dielectricis functional from DC to 10 GHz, from 3 THz to 50 THz and from 120 THzto 1400 THz. Additionally, halides such as cesium iodide are usable from4 THz to 1200 THz.

In general, the mixing signal from the embodiments shown in FIGS. 1-3 isgreatest when the applied static field is near the upper limit that maybe used for a given pointed electron-emitting tip. This effect is due tothe fact that the ratio of the mixer current to the DC current isdecreased as the static field is increased, since the ratio of theoptical to the static electric field is decreased. However, the increasein the DC current as the static field is increased is so great that itovercomes the first effect, and thus the net effect is an increase inthe current of the mixing signal.

FIG. 4 is an embodiment of the present invention that is configured as ahigh-speed switch gated by an optical pulse. In addition to mixing, theembodiments shown in FIGS. 1-3 may also be used for switching. Forexample, they may be used in high-speed logic circuits as AND gatesbecause the mixing signal will only be present when both lasers are on.Additionally, the embodiments in FIGS. 1-3 may be used as OR gates ifthe two lasers are each amplitude modulated at the desired frequency forthe output.

Returning to FIG. 4, a high-speed optically gated switch is shown, whichincludes an evacuated chamber 50 housing a collector 60, a pointedelectron-emitting tip 65, a dielectric waveguide 165 coated with adielectric layer 170 starting near the pointed tip 65, and an RF choke,which may be embodied in a sudden change in the impedance of the DCcoupling wire 175 such as a sudden change in the wire radius. Thehigh-speed gated switch also includes a laser 115, a lens system 140,and bias circuitry 80. Absent from the embodiment shown in FIG. 4 is aspherical mirror to intensify the input optical pulse because the use ofan external cavity would decrease the speed of the response. Theoperation of the high-speed optically gated switch is similar to theoperation described in conjunction with FIGS. 1-3. That is, the externalcircuitry 80 biases the electron-emitting tip 65 and the tip isirradiated with optical energy from a laser 115. The combination of thebias and the optical field stimulates electron emission from the tip 65.The electron emission creates a high frequency signal that is coupledout of the evacuated chamber 50 to a load 105, via the dielectricwaveguide 165. This embodiment functions like a high speed, highbandwidth transistor. That is, the optical signal gates the output ofthe device just as the base of a transistor gates the output of atransistor.

A device such as shown in FIG. 4 has numerous advantages over Austonswitches in that the device of the present invention is more than 50times faster than an Auston switch. The present invention is also lesssensitive to ionizing radiation and less sensitive to changes in theambient temperature than an Auston switch.

It is contemplated that a pointed electron-emitting tip, a transition,and a means to couple the high frequency signal out of the evacuatedchamber may be integrated into one structure. This integration may beaccomplished using, for example, silicon or any other suitable material.Roughened silicon having micro-protrusions, macro-outgrowths orsupertips may be used as a pointed electron-emitting tip, whileintrinsic silicon from the same wafer may be used as a dielectrictransition to support the Goubau wave. To produce a static field, thesilicon may be doped to conduct the DC current. Additionally, an antennasuch as a traveling wave log-periodic antenna may be fabricated fromanother portion of the silicon wafer. This configuration decreases thesize and increases the accuracy and efficiency of devices constructedaccording to the present invention. Diamond-like carbon, gallium nitrideand aluminum nitride are efficient field emitters that may be doped foruse in monolithic fabrication.

Of course, it should be understood that a range of changes andmodifications can be made to the preferred embodiments described above.For example, in applications requiring considerable frequency agility,it may be necessary to reduce the total gain caused by use of thequantum resonance, optical cavities, and surface plasmons, but inapplications requiring an extremely stable output, such as a localoscillator for mixing, it would be necessary to adjust these effects tomaximize the quality factor. For applications at operating frequenciesbelow 10 GHz it would be more convenient to couple the high frequencyenergy to the load by connecting a transmission line to a resistor ortransformer that is connected in seris with the circuit, and locatedeither inside or outside of the evacuated chamber, instead of usingGoubau lines, antennas, or dielectric waveguides. Two or more functionscan be performed by having more than one device in a single evacuatedchamber, or by having three or more optical sources used with a singletip. For example, two lasers may be mixed to provide a local oscillatorsignal to be mixed with a high frequency input signal for coherentdetection. This could be accomplished by using two separate devices in asingle evacuated chamber, or by using three-wave mixing with a singletip. It is therefore intended that the foregoing detailed description beregarded as illustrative rather than limiting and that it be understoodthat it is the following claims, including all equivalents, which areintended to define the scope of this invention.

We claim:
 1. An optoelectronic device comprising:A) an evacuated chambercontaining a negatively-biased source electrode having a pointed tip foremitting electrons and a coating on the source electrode forintensifying the effect of an optical field impinging on the sourceelectrode by creating surface plasmons when the source electrode isirradiated by an optical field; B) a laser generator for emitting anoptical field that is focused on the pointed tip of said sourceelectrode for stimulating emission of rapidly varying electrical currentfrom the pointed tip of the source electrode; and C) means responsive tothe rapidly-varying electrical current for coupling said current outsideof said evacuated chamber.
 2. The device of claim 1, wherein the opticalfield from the laser generator has a resonant interaction with thepointed tip.
 3. The device of claim 1, wherein the source electrodecomprises zirconium carbide.
 4. The device of claim 1, wherein thesource electrode comprises gallium nitride.
 5. The device of claim 1,wherein the source electrode comprises aluminum nitride.
 6. The deviceof claim 1, wherein the source electrode comprises diamond-like carbon.7. The device of claim 1, wherein the source electrode comprisesmolybdenum silicide.
 8. The device of claim 1, wherein the sourceelectrode comprises silicon fibrils.
 9. The device of claim 1, whereinthe source electrode comprises metal carbide.
 10. The device of claim 1,wherein the source electrode comprises hafnium carbide.
 11. The deviceof claim 1, wherein the pointed tip comprises micro-protrusions.
 12. Thedevice of claim 1, wherein the pointed tip comprises macro-outgrowths.13. The device of claim 1, wherein the pointed tip comprises a supertip.14. The device of claim 1, wherein the coating for intensifying theeffect of an optical field comprises silver.
 15. The device of claim 1,wherein the coating for intensifying the effect of an optical fieldcomprises aluminum.
 16. The device of claim 1, wherein the coating forintensifying the effect of an optical field comprises gallium.
 17. Thedevice of claim 1, wherein the coupling means comprises a Goubau line.18. The device of claim 1, wherein the coupling means comprises atraveling wave log-periodic antenna.
 19. The device of claim 18, furthercomprising an elliptical mirror for enhancing the effectiveness of thecoupling means.
 20. The device of claim 1, wherein the laser generatoris integrated into the evacuated chamber.
 21. The device of claim 20,wherein the optical field from the laser generator intersects the axisof the pointed tip at approximately 15°.
 22. The device of claim 1,wherein the coupling means comprises a dielectric waveguide.
 23. Thedevice of claim 22, wherein the dielectric waveguide comprises quartz.24. The device of claim 22, wherein the dielectric waveguide comprisesaluminum nitride.
 25. The device of claim 22, wherein the dielectricwaveguide comprises silicon.
 26. The device of claim 22, wherein thedielectric waveguide comprises germanium.
 27. The device of claim 22,wherein the dielectric waveguide comprises diamond-like carbon.
 28. Thedevice of claim 1, wherein the pointed tip and the coupling means areintegrated together onto a substrate.
 29. The device of claim 1, whereinthe source electrode and the coupling means are supported within theevacuated chamber using membrane technology.
 30. The device of claim 1,wherein the source electrode and the coupling means are supported withinthe evacuated chamber using filament technology.
 31. The device of claim1, wherein the coupling means comprises a transmission line connectedacross a resistor that is connected in series with the pointed tip. 32.The device of claim 1, wherein the coupling means comprises atransmission line connected a transformer that is connected in serieswith the pointed tip.
 33. An optoelectronic device comprising:A) anevacuated chamber containing a negatively-biased source electrode havinga pointed tip for emitting electrons and a coating on the sourceelectrode for intensifying the effect of an optical field impinging onthe source electrode by creating surface plasmons when the sourceelectrode is irradiated by an optical field; B) a laser generatoradapted to emit an optical field that is focused on the pointed tip ofsaid source electrode to stimulate emission of rapidly varyingelectrical current from the pointed tip of the source electrode; and C)a Goubau line adjacent the pointed tip, wherein the Goubau line isadapted to couple the rapidly-varying electrical current outside of theevacuated chamber.
 34. The device of claim 33, wherein the optical fieldfrom the laser generator has a resonant interaction with the pointedtip.
 35. The device of claim 33, further comprising a load and a horntransition adjacent the Goubau line, wherein the horn transition isadapted to provide an impedance match between the Goubau line and theload.
 36. The device of claim 35, wherein the source electrode compriseszirconium carbide.
 37. The device of claim 35, wherein the sourceelectrode comprises gallium nitride.
 38. The device of claim 35, whereinthe source electrode comprises silicon fibrils.
 39. The device of claim35, wherein the pointed tip comprises micro-protrusions.
 40. The deviceof claim 35, wherein the coating for intensifying the effect of anoptical field comprises silver.
 41. The device of claim 35, wherein thecoating for intensifying the effect of an optical field comprisesaluminum.
 42. The device of claim 35, wherein the coating forintensifying the effect of an optical field comprises gallium.
 43. Anoptoelectronic device comprising:A) an evacuated chamber containing anegatively-biased source electrode having a pointed tip for emittingelectrons and a coating on the source electrode for intensifying theeffect of an optical field impinging on the source electrode by creatingsurface plasmons when the source electrode is irradiated by an opticalfield; B) a laser generator adapted to emit an optical field that isfocused on the pointed tip of said source electrode to stimulateemission of rapidly varying electrical current from the pointed tip ofthe source electrode; and C) a transmission antenna adjacent the pointedtip, wherein the transmission antenna is adapted to radiate therapidly-varying electrical current outside of the evacuated chamber. 44.The device of claim 43, wherein the optical field from the lasergenerator has a resonant interaction with the pointed tip.
 45. Thedevice of claim 43, wherein the transmission antenna comprises atraveling wave log-periodic antenna.
 46. The device of claim 43, whereinthe laser generator is integrated into the evacuated chamber.
 47. Thedevice of claim 43, wherein the optical field from the laser generatorintersects the axis of the pointed tip at approximately 15°.
 48. Thedevice of claim 43, further comprising a reception antenna and a load,wherein the reception antenna is coupled to the load and is adapted toreceive the rapidly-varying electrical current radiated by thetransmission antenna.
 49. The device of claim 48, wherein the receptionantenna comprises a traveling wave log-periodic antenna.
 50. The deviceof claim 48, further comprising an elliptical mirror for intensifyingthe effectiveness of the coupling between the transmission antenna andthe reception antenna.
 51. An optoelectronic device comprising:A) anevacuated chamber containing a negatively-biased source electrode havinga pointed tip for emitting electrons and a coating on the sourceelectrode for intensifying the effect of an optical field impinging onthe source electrode by creating surface plasmons when the sourceelectrode is irradiated by an optical field; B) a laser generatoradapted to emit an optical field that is focused on the pointed tip ofsaid source electrode to stimulate emission of rapidly varyingelectrical current from the pointed tip of the source electrode; and C)a dielectric waveguide adjacent the pointed tip, wherein the dielectricwaveguide is adapted to couple the rapidly-varying electrical currentoutside of the evacuated chamber.
 52. The device of claim 51, whereinthe optical field from the laser generator has a resonant interactionwith the pointed tip.
 53. The device of claim 51, wherein the dielectricwaveguide comprises quartz.
 54. The device of claim 51, wherein thedielectric waveguide comprises aluminum nitride.
 55. The device of claim51, wherein the pointed tip and the dielectric waveguide are integratedtogether onto a substrate.
 56. The device of claim 51, wherein thesource electrode and the dielectric waveguide are supported within theevacuated chamber using membrane technology.
 57. The device of claim 51,wherein the source electrode and the dielectric waveguide are supportedwithin the evacuated chamber using filament technology.